Over the past 40 years, crude petroleum from the Niger-Delta area of Nigeria has become the main engine of Nigeria's economic development and industrialization, and also a significant source of petroleum-crude supply to the world. The exploration and exploitation of crude petroleum in the Niger-Delta oil/gas fields releases significant levels of methane (CH4]) and other volatile hydrocarbons into the troposphere, which photochemically react with nitrogen dioxide and water vapor to form ozone and smog in the troposphere. Handicapped by unavailability of ultraviolet (UV) absorption ozone analyzer for the experimental monitoring of the concentrations and trends of ozone, and possibly other air pollutants from photolysis (photochemical reaction) in the Niger-Delta troposphere, a theoretical attempt involving the use of basic chemistry stoichiometry was applied in estimating the magnitude of ozone and smoggy chemical. Therefore, this article examines the formation in the troposphere of photochemical smog from petroleum-methane and hydrocarbon emissions, and estimates the quantities of photochemical ozone and smog formed from the hydrocarbon emissions. To this end, the chemistry of photochemical smog formation was formulated on the basis of literature review, and the stoichiometric functions were developed using basic chemistry methods of calculating masses from balanced chemical equations. These were applied in estimating the quantities of tropospheric ozone and smog formed from the hydrocarbon emissions in the Niger-Delta oil fields as this article will show. Consequently, the annual trend of photochemical smog quantities and ozone magnitudes are presented and discussed.